1. Field of the Invention
The present invention relates generally to air conditioning systems and, more specifically, to an air conditioning (A/C) system and method of controlling the A/C system.
2. Description of the Related Art
It is known to provide an air conditioning (A/C) system for a vehicle. Typically, the A/C system is used to control cooling in an interior, cabin, or occupant compartment of the vehicle. The A/C system generally includes a condenser, compressor, evaporator, and expansion valve to remove heat from air and cool the air to the occupant compartment. The A/C system may include a desiccant dryer to remove moisture from the air.
It is also known to provide a mechanism to regenerate desiccant materials in the desiccant dryer by heating them and boiling off water vapor. An example of desiccant air conditioning for a motorized vehicle is disclosed in U.S. Pat. No. 6,029,462 to Denniston. In this patent, a complicated array of desiccant wheels and enthalpic wheels are required to regenerate the desiccant materials. However, this is difficult to achieve from a packaging standpoint in a motor vehicle. Also, in these systems, the only heat source sufficient to burn off the water vapor is engine exhaust, which is undesired.
An alternative to heating the desiccant materials of the desiccant dryer is to use vacuum to boil off the water vapor. A motor vehicle has vacuum available for most operating conditions. However, in a vacuum strategy, an important factor is the regeneration frequency. In order to boil off the water vapor, it is necessary to cycle rapidly between adsorption and desorption stages. This is necessary because desorption is an endothermic process. In a near vacuum, there is no mechanism to provide the heat required.
As a result, it is necessary to cycle the system according to the equation:   f  =                    m        H2O            *      Δ      ⁢              xe2x80x83            ⁢              h        vaporisaton                            m        desiccant            *              Cp        dessicant            *              (                              T            evap                    -          32                )            
Otherwise, the water present in the desiccant dryer will ice up and prevent further desorption. Therefore, there is a need in the art to provide an air conditioning system and method of controlling the air conditioning system to cycle the desiccant dryer.
Accordingly, the present invention is an air conditioning (A/C) system for a vehicle. The A/C system includes an evaporator, a desiccant dryer located downstream of the evaporator, and a compressor fluidly connected to the evaporator. The A/C system also includes a plurality of sensors to provide inputs relating to temperature of the evaporator and relative humidity of an occupant compartment of the vehicle. The A/C system further includes an electronic control unit electrically connected to the sensors to receive the inputs therefrom and electrically connected to the desiccant dryer and the compressor to turn the desiccant dryer and the compressor On and Off to control the temperature and relative humidity of air to the occupant compartment.
One advantage of the present invention is that an A/C system having a desiccant dryer is provided t o control relative humidity of air in an occupant compartment of a vehicle. Another advantage of the present invention is that the A/C system also includes a variable displacement compressor Yet another advantage of the present invention is that a method is provided for regeneration of a desiccant dryer of the A/C system. Still another advantage of the present invention is that the A/C system receives inputs from a plurality of sensors such as a humidity sensor, sunload sensor, temperature sensors, etc. and provides outputs to cycle the desiccant dryer On and Off to regenerate the desiccant materials.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings.